Troubleshooting Brake Controller Installations

Even the most experienced installer will encounter it from time to time: the brake controller installation is finished, the wires have all been run, but something is going wrong. Whether your controller is showing an error message or the trailer brakes just aren't working, there are a number of troubleshooting techniques you can use to get the problem fixed and get back on the road. Using the following information and testing procedures, you should be able to pinpoint and eliminate the most common issues encountered during and after a brake controller installation.

Common Brake Control Issues

ProblemPossible IssuesTesting Procedures
Brake controller display does not show that trailer is connected.
  1. Short on brake signal wire, trailer or vehicle side.
  2. Corrosion in trailer and/or vehicle plug.
  3. Short on brake magnets on trailer.
  4. Malfunctioning brake magnet(s).
Brake controller loses connection to battery ground.
  1. Ground wire was not connected to negative battery terminal, ground area does not have solid connection to ground.
  2. Adapter wiring does not match OEM connector on vehicle.
  3. Ground connection to negative battery terminal is loose.
  4. Ground wire has been damaged and exposed wiring is touching a metal area.
Brakes are applying too aggressively for the brake controller settings.
  1. Brake assemblies are not properly adjusted.
  2. Boost/Gain on brake controller is set too high for trailer size.
  • Adjust brakes properly (see video).
  • See brake control owner's manual for proper boost/gain settings for trailer size.
Trailer brakes only work with manual control, not with brake pedal. (Be sure to test for proper brake controller function with unloaded trailer in a safe area where you can reach low road speed before you determine that the brake controller is not working)
  1. Incorrect stoplight wire connection.
  2. Adapter wiring layout does not match OEM connector on vehicle.
Brake controller detects an overload condition during use.
  1. Trailer has too many brakes for brake controller to handle.
  2. Corrosion in trailer and/or vehicle plug.
  3. Brake signal wire on trailer is damaged, exposed wiring is touching metal area or another circuit.
  4. Malfunctioning brake magnet(s).
Display is erratic while braking.
  1. Short to battery on 12V wire connection.
  2. Short on brake signal wire, trailer or vehicle side
  3. Corrosion in trailer and/or vehicle plug.
  4. 12V wire was not connected to vehicle battery, 12V source used is not constant.
Brake controller detects a short on the brake wire while vehicle is idling.
  1. Corrosion in trailer and/or vehicle plug.
  2. Brake signal wire on trailer or vehicle is damaged, exposed wiring is touching metal area.
Trailer brakes engage when it is plugged into the vehicle.
  1. Incorrect stoplight wire connection.
  2. Corrosion in trailer and/or vehicle plug.
  3. Adapter wiring does not match OEM connector on vehicle.
Brake controller does not turn on.
  1. Connection to battery is not complete.
  2. Vehicle is missing a fuse or relay required to power 12V power circuit.
  3. Adapter wiring layout does not match OEM connector on vehicle.
  • Method 1
  • Check fuse block for missing fuse/relay. See vehicle-specific FAQ if available, or check owner's manual.

Basic Testing Procedures

Method 1: Verifying Correct Wire Connections (Hard Wire Installs)

Testing the Stoplight WireBrake Control Wire Colors

Wiring Adapter vs. OEM Connector

Method 1: Verifying Correct Wire Connections (Plug-in Installs)

Method 2: Testing for the Brake Signal

Testing the Blue Wire

Method 3: Looking for a Short or Ground Issue

Damaged Wiring

Method 4: Inspecting the Brake Assemblies

Brake Magnets

For more information, see:

Updated by: Raymond P.

Last updated: 7/5/18

Questions and Comments about this Article


Does the black wire have to be connected to battery? I would like to wire to ignition so the small led light does not cause the battery to die?

Reply from Chris R.

The brake controller needs the constant and reliable power that can only be provided by wiring it directly to the battery. That pesky LED light makes a lot of people nervous, but I can assure you that it doesn't draw enough power to cause any issues. It would take months and months (and months) of the vehicle sitting idle for it drain the battery. 58302


trailer brakes wont work through controller. but will work when you pull trailer disconnect. hook to different truck and brakes lock up immediately. is there supposed to be power on the trialer stop wire when brakes are applied

Reply from Chris R.

There definitely should be power on the brake output wire when applying the brakes in the tow vehicle. If you're using a proportional brake controller though you will only get power if you're actually moving (not just when testing in the driveway). Have you checked to see if the brakes lock up when applying the manual override on the controller? 57972

Dave M.

With no trailer connected i have 4.4 volts at trailer brake pin on truck side. is this right?

Reply from Chris R.

A trailer brake controller will constantly send small pulses of voltage back to the 7-Way - with or without a trailer attached. It's basically the controller's way of playing "Marco Polo" to detect if/when a trailer is connected. This is completely normal and while 4.4 volts might be a LITTLE more than usual, as long as it's not causing any problems when towing (your brakes aren't engaging when they shouldn't be) it's not something you need to worry about. 57592

Brent M.

I tow a triple axle hydraulic dump bed with a Chevy 2500 HD diesel. Factory trailer tow package and controller. It’s always towed fine, this first time it’s happened. No I haven’t pulled it again, but want to soon. As soon as I do I’ll let you know. It’s been a muddy as heck in KS, should dry up in a few days. Thanks

Reply from Chris R.

Sounds good. That exposed portion of wire you found could have just been causing a short, so hopefully it's all fixed up now. Just let me know if you run into any issues again! 57489

Brent M.

Trailer brakes intermittently engage while driving. Seems perhaps the bumps in the road cause this, maybe not. One thing for sure they lock up and disengage causing truck to downshift immediately and all gauges to . Checked wiring and found bare spot, I insulated the conductor and made sure all grounds had good metal connections. What do you think though ?

Reply from Chris R.

Have you towed again since locating and repairing the bare spot you mentioned on the wiring? What model brake controller are you using (or is it a factory unit)? Depending on the model, and if it's a proportional unit, I wonder if the sensitivity needs to be decreased a bit. It might just be sending back power every time you decelerate even a little. Let me know what you find and we can go from there! 57474


Why does my breaks lock up when I turn key on my controler pWorks perfect until I turn on my key then it locks up breaks on trailer.

Reply from Jacob H.

If your brakes are locking up as soon as you turn the key in the on position, then it means that you have constant 12V power going to the break output from an ignition source. I would check your wiring and rewire it if this is the case. The best way to test the wires is to use a circuit tester # 40376 to make sure you are getting the right signals going to the correct wires on the back of the brake controller. Another potential problem could be the pins may have corrosion on the 7-pole plug. What can happen is the pins will corrode eventually causing them to cross. In your case you would have the 12V pin crossing with the break signal pin. If this is the case cleaning the pins off should solve your issue. 55388

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